OFF-STAGNATION TESTS OF ESA IXV TPS INTERFACES IN PLASMATRON

Giuseppe Ceglia (1), Eduardo Trifoni (1), Jean-Baptiste Gouriet (2), Olivier Chazot (2), Vincenzo Mareschi (3), Giuseppe Rufolo (4), Giorgio Tumino (5)

(1) Centro Italiano Ricerche Aerospaziali, via Maiorise 81043 Capua (Italy), g.ceglia@cira.it, e.trifoni@cira.it (2) Von Karman Institute, Chausée de Waterloo 72 1640 Rhode-St-Genèse (Belgium), gouriet@vki.ac.be,

olivier.chazot@vki.ac.be (3) Thales Alenia Space Italia, Strada Antica di Collegno 253 10146 Torino (Italy),

vincenzo.mareschi@thalesaleniaspace.com (4) CIRA/ASI Technical Assistance to ESA, g.rufolo@cira.it

(5) European Space Agency, 8-10 rue Mario Nikis 75738 Paris (France), giorgio.tumino@esa.int

ABSTRACT An experimental investigation related to the Thermal Protection System (TPS) interfaces of the Intermediate eXperimental Vehicle (IXV) has been carried out in the Plasmatron facility at the von Karman Institute for Fluid Dynamics. The objective of this test campaign is to qualify the thermal behaviour of two different TPS interfaces under flight representative conditions in terms of heat flux and integral heat load (~180kW/m2 for 700 seconds). Three test samples are tested in off-stagnation configuration installed on an available flat plate holder, at the same test conditions. The first junction is composed of an upstream Ceramic Matrix Composite (CMC) plate and an ablative P50 cork composite block separated with a gap of 2mm. The second one is made of an upstream P50 block and a downstream ablative SV2A silicon elastomer block with silicon filler in between. A sample composed of P50 material is tested in order to obtain reference results without TPS interface effect. The overheating at the CMC-P50 interface due to the catalytic jump of the materials and the recession/swelling behaviour of the P50-SV2A interface are under investigation. All the test samples withstand relatively well the imposed heat flux for the test duration. As expected, both the ablative materials undergo a thermal degradation. The P50 exhibits the formation of a porous char layer and its recession; on the other hand the SV2A swells and forms a fragile char layer. 1. INTRODUCTION On February 11, 2015, the ESA (European Space Agency) IXV (Intermediate eXperimental Vehicle), leaded by TAS-I (Thales Alenia Space-Italy) as prime contractor, successfully completed its 100 minutes space mission. In particular, European capabilities in hypersonic un-powered manoeuvring re-entry flight of a lifting configuration have been verified. This vehicle is an atmospheric re-entry demonstrator conceived to perform a sub-orbital flight and to re-enter the atmosphere at 7.5km/s speed. During its mission, the vehicle served as an in-flight laboratory for the qualification of vehicle subsystems and systems, and to

provide another source of data on fundamental hypersonic phenomena for validation of tools, databases and design processes. Space vehicles re-entering in a planetary atmosphere undergo severe environment flight conditions due to aerothermodynamic loads impinging on the exposed surfaces [1]. Thus, development of specific Thermal Protection System (TPS) is required. Depending on the flight altitude and Mach number, the flow around the vehicle is characterized by the presence of dissociation and ionization phenomena due to the conversion of kinetic energy into thermal energy [2]. The environment across the shock waves results in a chemically reactive flow interacting with the walls. When dissociated species approach the heat shield, this interaction influences their recombination in exothermic reactions depending on the catalytic nature of the TPS. In this scenario, catalytic processes lead to the concept and design of the TPS materials. Indeed, the TPS material influences the performance of the heat shield promoting the catalytic processes along with other mechanisms, i.e. radiative effects and oxidation/nitridation phenomena [3]. The combination of different TPS materials in complex assemblies introduces variations of heat flux distribution due to discontinuities of catalytic properties at the interfaces [4]. Nearby to these interfaces, overheating effects can be induced by variations of recombination rate of the reacting species. The scope of this work is related to the activities of the TPS qualification for the IXV project. The objective of this test campaign is to collect plasma wind tunnel data to investigate two different material interfaces used in IXV TPS. In particular, the first junction is composed of Ceramic Matrix Composite (CMC) material, located upstream to an ablative material P50 cork composite. The second junction is based on two ablative materials P50 and SV2A silicon elastomer. The sample assembling, the operating conditions and the test procedure are described in the following sections. Furthermore, the test results are investigated in terms of TPS performance qualification.

X=110mm, Qw=180kW/m²

Figure 1. Off-stagnation heat flux distribution with

respect to the axial coordinate (Qst=597kW/m², P=1500Pa) [6]

2. EXPERIMENTAL SETUP The experiments are conducted in the Plasmatron facility at the von Karman Institute for Fluid Dynamics (VKI). The Plasmatron is a high enthalpy wind tunnel, equipped with a high power, high frequency and high voltage (1.2MW, 400kHz, 2kV) solid state generator. A 160mm diameter plasma torch provides a plasma jet in a 2.5m long, 1.4m diameter test chamber. A holding probe allows for the investigation of TPS materials and a Stagnation Point (SP) heat flux probe is used for the flow characterization. They are mounted on two water-cooled arms that can be injected into and out of the flow by a hydraulic displacement mechanism. The experimental campaign is carried out by applying off-stagnation testing methodology described in [5]. Off-stagnation configuration is realized by using a Flat Plate (FP) probe. Such probe offers flight representative test conditions for boundary layer investigation. The FP consists of a copper plate mounted on a swinging-in water cooled arm. The plate has a 12.5mm radius rounded nose. The plate spanwise dimension is of ~200mm. A groove with a width of 30mm, a length of 189mm and a depth of 22.5mm allows for the installation of a test sample or a linear calorimetric element [6]. Viladegut [6] performed calibration tests by using intrusive measurements techniques to characterize the flow field at different operating conditions. Several off-stagnation heat flux distributions have been measured at static pressure chamber of P=1500Pa for different mass flow rates and stagnation heat flux. One of these distributions, i.e. air mass flow of 16g/s and stagnation heat flux Qst of 597kW/m2, matches with the present test requirements. The test operating requirements reproduce flight representative conditions in terms of heat flux and integral heat load, i.e., ~180kW/m2 fully catalytic cold wall condition at the TPS interface for 700 seconds. The test conditions are summarized in Tab. 1. The

Figure 2. Schematic of the holder and samples: position

of the contact thermocouples (cut view along the centreline)

Table 1: Operating conditions Static pressure 1500Pa Gas mixture Standard Air Mass flow rate 16g/s Stagnation heat flux 597kW/m² Dynamic pressure (measured in [6]) 336Pa Total Enthalpy 11.7MJ/kg Velocity 840m/s Temperature 4715K Off-stagnation heat flux at x = 110mm 180kW/m²

corresponding streamwise distribution of the heat flux is plotted in Fig. 1, extracted from [6]. In Fig. 2, four type E thermocouples (TCs), i.e., TC1E, 2E, 3E and 5E, measure the contact temperature on the back wall of the test sample at different positions. An additional one, i.e., TC4E, is positioned on the other side of a Teflon plate in order to monitor the temperature of the water-cooled flat plate during the experiments. The TCs have a typical uncertainly of +/-0.2K. The positions of the TCs along the centreline of test samples are shown in Fig. 2. The TCs are installed on the Teflon plate into a groove built along the centreline. A schematic view of the experimental setup is depicted in Fig. 3 with the respective positions of the optical instruments and water cooled probes, i.e., FP and the SP probes. Three optical accesses at Plasmatron test chamber enable non-intrusive diagnostics to probe the flow and the test samples: the lateral windows allow for perpendicular side views of the plasma jet and probes, and the torch-side window allows for a frontal oblique view of the TPS surface.

Figure 3. Schematic view of the experimental setup

Figure 4. CMC-P50 (top) and P50-SV2A (bottom) sample (left) before and after installation (right)

A two-colour pyrometer, an infrared (IR) camera and a video camera have been mounted in correspondence of these optical accesses. The two-colour pyrometer points to the surface sample at location ~124mm from the leading edge of the flat plate. The operating temperature ranges between 700-1800°C; Panerai [3] has estimated its overall uncertainty at ±10% in the lowest temperature range. A quartz window of 18mm thick is located at ~1.0m from the test sample. The size of the target spot at 1.0m from the target is ~12mm (magnification of 82:1). The pyrometer is inclined ~9° with respect to the surface normal. A blackbody reference source (Landcal R1500T, Land Instruments International) has been used to calibrate the two-colour pyrometer taking into account the presence of the window through the optical path. The temperature measured by the two-colour pyrometer is considered as real surface temperature being emissivity independent. In order to measure the distribution of the temperature over the surface sample, the test models are observed by the IR camera (ThermaCAM SC3000, FLIR systems) with a 320x240 resolution and a maximum spectral sensitivity at 8-9µm. The IR camera measures in the range of temperature between 350-1500°C with an acquisition rate of 50kHz. The IR thermogram is

imaged through a KRS-5 window of 18mm thick located at ~1.0m from the test sample. The sensor is inclined ~3.5° with respect to the surface normal. The same calibration procedure performed for the two-colour pyrometer has been applied for the IR camera. It is worth to note that all the investigated materials are characterized by a total hemispherical emissivity of 0.8. This value is set for the reduction of the IR data.

2.1. Test samples Three different test samples are investigated under the same test conditions. The first test sample is composed of P50 cork composite material produced by Amorin Cork Composite [7]. The second sample is composed of a base made in P50 cork and a plate of 47mm streamwise length made of CMC material manufactured by Safran Herakles. As for the P50 sample, a dovetail joint is the technical solution for the fixation of the P50 base and of CMC plate on the FP holder. A gap of 2mm is placed between CMC and P50 materials. This junction is at 110mm from the leading edge of the FP holder. It is worth mentioning the internal geometry of the gap reproduces the TPS flight interface configuration (Fig. 2). Fig. 4 (top) shows the CMC-P50 sample before (left) and after installation on FP holder (right). The third sample is composed of two different ablative materials, i.e., P50 and a silicone elastomer based material SV2A manufactured by AVIO. They compose two parallelepiped blocks installed in series as shown in Fig. 2. P50 block is located upstream with respect to the SV2A block. The width and depth of these elements are, respectively, 26mm and 20mm. Silicon based filler is applied at the junction between P50 and SV2A material (~3mm thick). The position of the junction is the same as for the CMC-P50 sample. An additional block of P50 material is installed downstream from the third test sample. This second junction (SV2A-P50) is without filler.

In Fig. 4 (bottom), note that two Teflon plates with a thickness of ~1.45mm are installed along the streamwise direction at sidewalls of the test sample. These technical solutions ensure a mechanical fixation of the sample on the FP holder.

3. RESULTS

3.1. P50 test Fig. 5 shows two pictures extracted from the video sequence. The picture on the left corresponds to the beginning of the test when the sample is injected into the plasma flow. The picture on the right corresponds to the end of the test, i.e., 700 seconds after the sample injection. The plasma jet is coming from the right. The ablation, which is released from the material, interacts with the boundary layer and radiates in the visible. It is worth to note the wavelengths from these radiating species (in the visible) change after a certain exposure time when the char surface appears.

Figure 5. Images extracted from the video sequence of the P50 test at (left) start and (right) end

Figure 6. Post-test pictures of the P50 sample

After the plasma exposure, on the entire surface of the test sample a black char layer is formed and surface recession appears, more pronounced in the front part of the sample due to a higher heat flux (Fig. 6). The finely cracked top surface is characteristic of cork-based materials [8]. The mass loss of the P50 test sample after 700 seconds under plasma exposure is of 16.348g, which represent 26.5% of the initial mass of the sample. The temperatures acquired by the TCs with respect to the time are plotted in Fig. 7. The temperatures increase continuously during the plasma exposure. A temperature jump occurs in the first few seconds of the exposure. After this jump, the temperatures continue to increase at a lower rate. Starting from ~125 seconds, the temperature gradient of the TCs 1E, 2E and 5E is similar. However, the temperature gradient of the TC 3E is lower within the first ~130 seconds and then it increases during the rest of the test duration. For the temperatures measured by the TCs 1E and 2E, a plateau at the end of the test is reached. The maximum temperatures detected by the TCs 1E, 2E, 3E and 5E are 82°C, 77°C, 76°C and 69°C, respectively. The streamwise pattern of the temperatures measured by the TCs is in agreement with the heat flux distribution plotted in Fig. 1. An overshoot is observed in the histories of the TCs 1E and 2E during the cooling down phase (~250 seconds after the end of the exposure to the plasma jet).

Figure 7. Time evolution of the temperature acquired by

the thermocouples for P50 sample

Figure 8. Time evolution of the temperature acquired by the two-colour pyrometer for the P50 sample, 5-order

polynomial fit curve is superimposed

Figure 9. Temperature surface distribution measured by IR camera (ε=0.8) at 350 sec after sample injection for P50 sample: iso-contour (top), centreline distribution

(bottom)

Fig. 8 plots the temperature measured by the two-colour pyrometer with respect to the time. The blue markers correspond to the measurement points while the black curve represents a 5-order polynomial fit. The surface temperature at the measurement spot increases in the first 500 seconds of the test from ~850°C up to ~992°C. It slightly decreases in the last 200 seconds of the test. It is worth to note the large scattering of the measurement points of +/-60°C around the fit curve is observed.

Fig. 9 shows the iso-contour of the IR temperature

Figure 10. Images extracted from the video sequence of the CMC-P50 test at (left) start and (right) end

Figure 11. Post-test pictures of the CMC-P50 sample

surface distribution at 350 seconds after the sample injection. The plasma flows from right to left. In the bottom, the temperature profile along the centreline of the sample is extracted from the IR temperature surface distribution. The axial-coordinate is the streamwise distance from the leading edge of the FP holder (Fig. 2). The highest temperature of ~1100°C is measured at ~71mm from the FP leading edge. The surface temperature decreases of ~200°C along the streamwise direction. Note that the temperatures measured by the two-colour pyrometer and IR camera are in good agreement to each other.

3.2. CMC-P50 test In Fig. 10, the images extracted from the video sequence at beginning (left) and 700 seconds (right) from the injection of the test sample show, as expected, that no visible radiating species are released from the CMC surface. Fig. 11 shows post-test pictures of the CMC-P50 sample. As expected, the surface of the cork exposed to the plasma flow presents characteristic cracked char surface. As for the P50 sample, the recession of char surface in the upstream part with respect to the CMC plate is higher. Just downstream the CMC plate, the recession forms a step-down profile (Fig. 11). A detailed post-test inspection of the junction between the CMC and the P50 material reveals that the slot geometry is well preserved. The P50 cork surface underneath the CMC plate is well preserved as well. The CMC plate shows different colour patterns at the

Figure 12. Time evolution of the temperature acquired

by the thermocouples for CMC-P50 sample

Figure 13. Time evolution of the temperature acquired by the two-colour pyrometer for the CMC-P50 sample,

5-order polynomial fit curve is superimposed

Figure 14. Temperature surface distribution measured by IR camera (ε=0.8) at 350 sec after sample injection for CMC-P50 test sample: iso-contour (top), centreline

distribution (bottom) surface. A bluish colour is also present on the two sides of the plate. It can be due to oxidation phenomena occurring over the surface of the CMC plate. Since the test sample is composed of two separable parts, the mass loss is evaluated for each individual element. The mass loss for the P50 block is 13,834g which represents 23.2% of its initial mass. The mass loss of the P50 material is lower than that measured in the P50 only test. The partial protection due to the CMC plate promotes the reduction of the mass loss. However, the CMC plate does not lose mass during the test. Fig. 12 plots the time evolution of the temperatures

acquired by the TCs for the CMC-P50 sample. As for the P50 test, the temperatures associated with the TCs 1E, 2E, 3E and 5E, show a similar trend. A temperature jump is measured in the first few seconds of the exposure. After this jump, the temperature continues to increase at a lower rate. Then the temperatures measured by the TCs 1E, 2E and 3E reach a plateau at the end of the test (~80°C). Note that the maximum temperature at the back wall of the sample is less than the maximum allowable temperature of 150°C at the cold structure. The temperature on the back wall of the test sample drops after the exposure time to the plasma jet. As for the P50 test, a slight overshoot is observed in the temperature time evolution after the plasma exposure. It is worth mentioning the initial temperature before the plasma exposure is higher of 5°C in this test than for the P50 test, i.e., ~33°C instead of 28°C, respectively. In Fig. 13, the temperature measured by the two-colour pyrometer is plotted with respect to the time. The pyrometer points to the P50 material at 13mm downstream the CMC-P50 interface (Fig. 2). The surface temperature downstream the junction increases up to a maximum value of ~1018°C within the first 350 seconds. As for the P50 test, the pyrometer data show large amplitude fluctuations due to the disturbance of the IR signal due to the species released from the P50 material. In Fig. 14, the iso-contour of the temperature distribution measured by the IR camera at 350 seconds after the injection of the CMC-P50 sample in the plasma jet is depicted. Heat sink effect occurs at the side wall of the CMC plate. It is caused by the dovetail joint of the CMC plate in contact with the copper FP holder. The maximum value of temperature reached at the surface of the CMC plate is of ~700°C.

3.3. P50-SV2A test In Fig. 15, the two pictures extracted from the video sequence reveal radiating species that emit in the visible as for the P50 test. Fig. 16 shows post-test pictures of the P50-SV2A sample before and after disassembling. In the picture on top, several pieces of the SV2A char layer are detached from the sample. These pieces detach during the cooling down phase. The remaining SV2A charred layer just downstream the junction is also very loose. The surface of the P50 material exposed to the plasma flow presents characteristic cracked char surface. A large recession is observed in the upstream P50 part of the sample. The filler between the P50 and SV2A ablative materials does not show any sign of mechanical degradation. The side and bottom views of the test sample show that the thermal waves slightly penetrate in the ablative material and in the filler bond in between. The mass loss for the block P50-SV2A is of 8.101g which represents 16.1% of its initial mass. The mass loss of the extra block in P50 material is 1.649g which represents 17.6% of its initial mass. It is worth to note

Figure 15: Images extracted from the video sequence of the P50-SV2A test at (left) start and (right) end

Figure 16. Post-test pictures of the P50-SV2A sample

the detached pieces are taken into account for the weight measurements. Fig. 17 plots the time evolution of the temperature acquired by the TCs for the P50-SV2A test. The time evolution of the temperature acquired by the TCs 1E, 2E, 3E and 5E shows similar trends. The temperature gradients of the TCs 1E and 5E are similar during the plasma exposure. However, different levels are reached according to the actual heat flux applied at their position. Note that the temperature acquired by the TC 1E seems to stabilise at the end of the test. The TC 5E located at 211mm from the leading edge of the FP is in contact with the extra P50 block. This block is exposed to the lowest heat flux and the TC 5E measures the lowest temperature. The maximum temperature measured by the TC 5E is of ~67°C. The highest maximum temperature is detected by the TCs 2E and 3E. The TC 2E is in direct contact with the filler whiles the TC 3E is in contact with the SV2A material. These two TCs measure exactly the same temperature during the plasma exposure and during the cooling down phase. The maximum temperature reached at these two locations after 700 seconds of plasma exposure is of 93°C; it is below the maximum allowable temperature of 150°C for the cold structure. Fig. 18 plots the temperature measured by the two-colour pyrometer. The blue markers correspond to the measurement points while the black curve represents

Figure 17. Time evolution of the temperature acquired

by the thermocouples for P50-SV2A sample

Figure 18. Time evolution of the temperature acquired by the two-colour pyrometer for the P50-SV2A sample,

5-order polynomial fit curve is superimposed

Figure 19. Temperature surface distribution measured by IR camera (ε=0.8) at 350 sec after sample injection for P50-SV2A test sample: iso-contour (top), centreline

distribution (bottom) to 5-order polynomial fit curve. The surface temperature at the target spot is almost constant (~950°C) in the first 350 seconds of the test, before decreasing in the second half (~875°C). The fluctuations of the pyrometer signal are lower for this test than for the P50 and CMC-P50. In this test, the measuring spot is on the surface of the SV2A block, instead of the P50. The species released from the cork P50 material disturb more the pyrometer signal in its infrared bandwidth. In Fig. 19, the iso-contour of the temperature distribution measured by the IR camera at 350 seconds after the injection of the sample in the plasma jet is

Figure 20. Comparison plot of the 5-order polynomial curves by fitting two-colour data: continuous line P50

and dotted line CMC-P50

depicted. The transition P50 to SV2A results in a temperature drop at 110mm from the leading edge of the FP holder.

3.4. Interface effects

Fig. 20 shows a comparison plot obtained by superimposing 5-order polynomial fit curves for the P50 and CMC-P50 tests. As previously shown for the P50 test, the temperature measured by the two-colour pyrometer reaches a maximum value about of 992°C. Assuming the radiative equilibrium condition is locally achieved, the heat flux re-irradiated from the surface Qrad is about of 116kW/m2, estimated by the Stefan–Boltzmann law (Eq. 1).

TwQrad4σε= (1)

Where the σ is the Stefan–Boltzmann constant and the Tw is the wall temperature. At the same test condition (11.7MJ/kg, 1500Pa), the calibrated heat flux [6] impinging at the location of the two colour pyrometer spot is of 160kW/m2 at cold wall condition (70°C). However, the impinging heat flux decreases to 147kW/m2 at hot wall condition (Tw=992°C) according to the Eq. 2.

wpw TcHQ −∝ 0 (2)

Where H0 is the total enthalpy at boundary layer, cp is the specific heat at constant pressure of the plasma (1.01kJ/kgK). Comparing the impinging heat flux at hot wall condition with respect to the heat flux re-irradiated from the surface, it is possible to find out that the contribution of ablation and conduction to the heat flux balance is about of 31kW/m2. Thus, the re-irradiate heat flux is 79% of the impinging one and the rest can be considered as ablation and conduction. Furthermore, the catalytic jump due to the CMC-P50 interface can be evaluated by comparing re-irradiated heat flux related to the maximum temperatures detected by the two-colour pyrometer for the CMC-P50 and P50 tests. As previously mentioned, the maximum temperature reached at the pyrometer spot location for the CMC-P50 test is of 1018°C. Assuming the radiative equilibrium condition is locally achieved also for CMC-

P50 test, the re-irradiated heat flux is of 126kW/m2. Thus, the effect on the re-irradiated heat flux due to the catalytic jump at the CMC-P50 interface is about of +10%; it is reasonable to assume the impinging heat flux accordingly increases. This overheating promotes also an increase of the recession rate according to the step-down geometry previously observed downstream from the interface for the CMC-P50 test (Fig. 11). In Fig. 20, this overheating is inhibited after 600 seconds; the final temperature for the CMC-P50 sample is lower than for the P50 sample. It can be due to a wake flow occurring in correspondence of the step-down geometry. In Fig. 18, the temperature reached on SV2A material during the plateau phase is about of 950°C. In radiative equilibrium condition at the pyrometer spot location, the heat flux re-irradiated from the surface is of 102kW/m2. The impinging heat flux decreases about to 148kW/m2 at hot wall condition (950°C) (Eq. 2). For the SV2A material, the contribution of ablation and conduction to the heat flux balance is about of 46kW/m2, i.e. roughly 69% of the impinging heat flux is balanced by re-irradiation and 31% by ablation and conduction. Furthermore, the maximum temperature detected at the first 30 seconds from the injection of the SV2A sample into the plasma flow is associated with the swelling of the SV2A material. It promotes the formation of a wake flow induced by the new shape of the P50-SV2A sample. The wake flow is also visible in Fig. 15 (right). In Fig. 16, the deposition of white particles coming from the upstream silicon based filler on the surface of FP holder gives a qualitative visualization of the spreading of the wake. In addition, these residual particles coat the surface of SV2A block and of downstream P50 one. 4. CONCLUSIONS Three test samples have been tested in off-stagnation configuration in Plasmatron facility at VKI in the framework of the IXV TPS activities. Two interfaces representative of the real TPS assemblies of the IXV have been investigated. The first junction is composed of an upstream CMC plate and an ablative P50 cork composite block separated with a gap of 2mm. The second one is made of an upstream P50 block and an ablative SV2A silicon elastomer based material block with silicon filler in between. A sample composed of P50 material is tested in order to obtain reference results without TPS interface effects. The three test samples have withstood relatively well the imposed heat flux. The qualification tests highlight the thermal behaviour of the TPS interfaces under flight representative conditions in terms of heat flux and integral heat load (~180kW/m2 for 700 seconds). Both ablative tested materials, P50 and SV2A, undergo an expected thermal degradation with the formation of a porous char layer. Recession of the char layer is detected for the P50 material. On the other hand, SV2A material swells in the first few seconds during the plasma exposure. The silicon-based filler applied

between the P50 and SV2A materials exhibits effects of thermal degradation on the surface; Heat sink effect due to the dovetail joint between the CMC plate and FP holder is observed. The maximum temperatures measured by the TCs at the back wall of the CMC-P50 and P50-SV2A interfaces, respectively of 80°C and 93°C, are less than the maximum allowable temperature of 150°C at the cold structure. For the P50 material, re-irradiated heat flux is 79% of the impinging heat flux. For the SV2A material, the re-irradiated heat flux contributes with 69% of the impinging heat flux. Recession/swelling behaviour has been observed as characteristic of the P50-SV2A junction when exposed to the plasma flow. For the CMC-P50 test, the catalytic jump due to the CMC-P50 interface determines an overheating about of +10% in terms of re-irradiated heat flux. A pronounced recession of the P50 material nearby the junction has been observed.

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